infoverload commented on a change in pull request #18813:
URL: https://github.com/apache/flink/pull/18813#discussion_r810102026
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File path: docs/content/docs/dev/table/types.md
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@@ -1487,6 +1481,88 @@ Not supported.
{{< /tab >}}
{{< /tabs >}}
+Casting
+-------
+
+Flink SQL can perform casting between a defined pair `from` type and `target`
type. While some
+casting operations can always succeed no matter the input value, others can
fail at runtime, that
+is, for some input values there is no way to create a value for the target
type. For example, it's
+always possible to convert `INT` to `STRING`, but viceversa is not true, as
you can provide an
+input `STRING` which cannot be converted to `INT`, like `'abc'`.
+
+Flink SQL, during planning, rejects queries which cast pairs are invalid with
+a `ValidationException`, e.g. when trying to cast a `TIMESTAMP` to an
`INTERVAL`, but the user needs
+to handle manually cases where a cast pair is valid, but can fail at runtime.
Review comment:
```suggestion
During the planning stage, Flink SQL rejects queries for invalid
pairs-to-be-casted that throw a
`ValidationException` (i.e. when trying to cast a `TIMESTAMP` to an
`INTERVAL`). Valid pairs-to-be-casted
that fail at runtime need to be handled manually.
```
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